Meeting Abstract

P2.159  Monday, Jan. 5  Melatonin, Aggression, and Social Dominance in the Black-Capped Chickadee KRIENGWATANA, B.P.*; AN, Y.; NEWMAN, A.E.; MACDOUGALL-SHACKLETON, E.A.; MACDOUGALL-SHACKLETON, S.A.; University of Western Ontario, London ON; University of Western Ontario, London ON; University of British Columbia, Vancouver BC; University of Western Ontario, London ON; University of Western Ontario, London ON bkrieng@uwo.ca

Non-breeding black-capped chickadees (Poecile atricapillus) form linear dominance hierarchies in the winter. Dominants establish and maintain status by repeatedly directing aggression towards subordinates. The mechanism underlying dominant-subordinate aggression is unclear, as testes are regressed and testosterone levels are assumed to be basal in non-breeding chickadees. Plasma levels of melatonin, an idolamine produced by the pineal gland in the absence of light, are higher during non-breeding conditions, and treatment with exogenous melatonin has been shown to facilitate aggression in some animals. This study investigated the role of melatonin in black-capped chickadee dominant-subordinate aggression and its possible effects on social status. Seasonal and circadian changes in plasma melatonin and testosterone concentrations in isolated, captive chickadees were measured in blood samples collected at 5 different times throughout the day and night, during breeding (16:8 L:D) and non-breeding (10:14 L:D) condition. To determine the relationship between melatonin and establishing and maintaining status, unfamiliar subjects were allowed to interact in pairs and blood was collected immediately after the interaction, 24 hours, and 10 days later. Future research will investigate whether exogenous melatonin treatment can increase aggression and subsequently alter social status. These studies thus test the hypothesis that dominance-related aggression is mediated by seasonal and individual differences in melatonin.